1. Field of the Invention
The present invention relates to an optical system and an optical apparatus having the same, and more particularly, to an optical system capable of being applied to, for example, a still camera, a video camera, a projector, a TV camera for broadcasting, a monitoring camera, and the like, and an optical apparatus having the same.
2. Description of the Related Art
Recently, in a photographic optical system used for an image pickup apparatus such as a video camera and a projection optical system used for an image projection apparatus such as a projector, as the number of pixels increases (implementation of a large number of pixels), or as the density of pixels increases (implementation of a high density of pixels), a corresponding optical system having high quality of image and high performance is needed.
In order to cope with a large number of pixels and a high density of pixels, it is important to allow particularly chromatic aberration of magnification among various aberrations of the optical system to be corrected well.
Japanese Patent Application Laid-Open No. 2004-020765 discusses, as an optical system used for a projector, a negative lead type zoom lens including a total of five lens units where a lens unit having a negative refractive power is disposed at the closest object side. The zoom lens includes, in order from an object side to an image side, a first lens unit having a negative refractive power, second to fourth lens units having a positive refractive power which are moved for variation of magnification and for correcting the variation of an image plane caused by the variation of magnification, and a fifth lens unit having a positive refractive power, which is stationary during the variation of magnification. In the zoom lens, in order to allow chromatic aberration of magnification to be corrected well over the entire zoom range, a glass material having a relatively high relative partial dispersion is used for a negative lens of the first lens unit.
Japanese Patent Application Laid-Open No. 2002-131640 discusses, as an optical system used for an image pickup apparatus, a positive lead type zoom lens coping with a large number of pixels and a high density of pixels, which includes, in order from an object side to an image side, a first lens unit having a positive refractive power, a second lens unit having a negative refractive power, and a third lens unit having a positive refractive power. In the zoom lens, in order to allow chromatic aberration of magnification to be corrected over the entire range, a glass material having a relatively high relative partial dispersion is used for a negative lens of the second lens unit.
In addition, Japanese Patent Application Laid-Open Nos. 2008-129403 and 2003-307672 discuss retro-focus type monofocal lenses, where in order to allow chromatic aberration of magnification to be corrected well over the entire object distance range, a glass material of which the relative partial dispersion θgF is relatively high in comparison with the Abbe number is used for a negative lens which is closer to the object side than an aperture stop.
As the number of pixels further increases and the density of pixels highly increases, in an optical system used for super high vision requiring, for example, 8000×4000 pixels as the number of pixels, a very small amount of aberration is required for various aberrations.
Particularly, with respect to chromatic aberration of magnification, an amount of chromatic aberration of magnification between g-line and F-line as well as an amount of chromatic aberration of magnification between C-line and F-line with respect to d-line as a reference is required to be very small. In order to reduce the amount of chromatic aberration of magnification between g-line and F-line, there is a need to consider an anomalous dispersion property (relation between Abbe number and relative partial dispersion (θgF value)) of the glass material used.
In the aforementioned optical system, in order to correct chromatic aberration of magnification, a lens unit having a negative refractive power is disposed closer to the object side than an aperture portion SP determining a maximum axial light flux diameter, and chromatic aberration of magnification in the lens unit is corrected. Herein, the “aperture portion determining the maximum axial light flux diameter” denotes an aperture portion determining an F-number in an axial light flux (light flux of which the principal ray propagates along an optical axis) when an object distance is at infinite distance.
In general, in many cases, an aperture stop functions as the aperture portion SP. However, in the case of a zoom lens having no mechanical aperture stop, the maximum axial light flux diameter may be determined by a portion of a lens barrel or an outer diameter of a specific lens. In this case, the portion of the lens barrel or the outer diameter of the lens functions as the aperture portion SP determining the maximum axial light flux diameter.
However, the aforementioned documents do not discuss relative partial dispersion (θgF) of a glass material used. Therefore, if a material corresponding to the refractive index and the Abbe number is applied to a general glass material, the following results can be deducted.
In Japanese Patent Application Laid-Open No. 2004-020765, a material of the negative lens of the first lens unit having a negative refractive power is configured by using a glass material having low dispersion and a material having high dispersion, so that chromatic aberration of magnification between g-line and F-line with the high dispersion property can be reduced while correcting chromatic aberration of magnification between C-line and F-line. Although the relative partial dispersion of the glass material used is not discussed, in terms of the refractive index and the Abbe number, a glass material corresponding to S-FPL51 (product name) manufactured by OHARA, INC. may be used for the first negative lens of the first lens unit in Example 3, and a glass material corresponding to S-NPH1 (product name) manufactured by OHARA, INC. may be used for the second negative lens.
These materials have a large anomalous dispersion property in comparison with other glass materials. According to this configuration, chromatic aberration of magnification is not necessarily sufficiently corrected.
In Japanese Patent Application Laid-Open No. 2002-131640, a material of the negative lens of the second lens unit having a negative refractive power is configured by using a glass material having low dispersion and a material having high dispersion, so that chromatic aberration of magnification between g-line and F-line with the high dispersion property can be reduced while correcting chromatic aberration of magnification between C-line and F-line. Although the relative partial dispersion of the glass material used is not discussed, in terms of the refractive index and the Abbe number, a glass material corresponding to E-FDS1 (product name) manufactured by HOYA CO., LTD. may be used for the first negative lens of the second lens unit in Example 1, and a glass material corresponding to S-FSL5 (product name) manufactured by OHARA, INC. may be used for the second negative lens thereof.
Although E-FDS1 (product name) is a glass material having a large anomalous dispersion property in comparison with other glass materials, S-FSL5 (product name) is a glass material having a low anomalous dispersion property. Therefore, the issue of the correction of chromatic aberration of magnification is not necessarily sufficiently solved.
In Japanese Patent Application Laid-Open No. 2008-129403, a material of the negative lens of the first lens unit having a negative refractive power is configured by mainly using a glass material having low dispersion and a large relative partial dispersion difference ΔθgF in the positive direction. Therefore, chromatic aberration of magnification between g-line and F-line can be reduced while correcting chromatic aberration of magnification between C-line and F-line. Although the relative partial dispersion of the glass material used is not discussed, in terms of the refractive index and the Abbe number, a glass material corresponding to S-FPL53 (product name) manufactured by OHARA, INC. may be used for the first to fourth negative lenses of the first lens unit in Example 5, and a glass material corresponding to S-NPH2 manufactured by OHARA, INC. may be used for the fifth negative lens thereof.
These glass materials have high relative partial dispersion in comparison with other glass materials and an anomalous dispersion property. The negative lens formed by using a material having high dispersion is disposed adjacent the aperture portion SP, so that chromatic aberration of magnification between g-line and F-line remains. Therefore, chromatic aberration of magnification is not necessarily sufficiently corrected.
In Japanese Patent Application Laid-Open No. 2003-307672, a material having a low dispersion and a material having a high dispersion are used for a negative lens which is closer to the object side than an aperture stop. However, chromatic aberration of magnification is not necessarily sufficiently corrected.